package tree;

import java.util.Objects;

/**
 * @author linzou@linkdoc.com
 * @ClassName: SegmentTree
 * @Description:
 * @date 2019/6/4 8:31 AM
 */
public class SegmentTree<E> {

    private E[] tree;
    private E[] data;
    private Merger<E> merger;

    public SegmentTree(E[] arr,Merger<E> merger){

        this.merger = merger;

        data = (E[]) new Object[arr.length];

        System.arraycopy(arr,0,data,0,arr.length);

        tree = (E[]) new Object[4 * arr.length];

        buildSegmentTree(0,0,data.length - 1);
    }


    /**
     * 在treeIndex的位置创建标识区间[l...r]的线段树
     * @param treeIndex
     * @param l
     * @param r
     * @return
     */
    private void buildSegmentTree(int treeIndex,int l,int r){

        if(l==r){
            tree[treeIndex] = data[l];
            return ;
        }

        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        int mid = l + (r - l) / 2;

        buildSegmentTree(leftTreeIndex,l,mid);
        buildSegmentTree(rightTreeIndex,mid + 1, r);

        tree[treeIndex] = merger.merge(tree[leftTreeIndex],tree[rightTreeIndex]);

    }


    public int getSize(){
        return data.length;
    }

    public E get(int index){

        if(index < 0 || index >= data.length){
            throw new IllegalArgumentException("Index is illegal.");
        }

        return data[index];
    }

    private int leftChild(int index){
        return 2 * index + 1;
    }

    private int rightChild(int index){
        return 2 * index + 2;
    }


    public E query(int queryL,int queryR){

        if(queryL < 0 || queryL >= data.length || queryR < 0 || queryR >= data.length || queryL > queryR){
            throw new IllegalArgumentException("Index is illegal.");
        }

        return query(0,0,data.length - 1,queryL,queryR);

    }

    private E query(int treeIndex,int l,int r,int queryL,int queryR){

        if(l == queryL && r == queryR){
            return tree[treeIndex];
        }


        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        int mid = l + (r - l) / 2;

        if(queryL >= mid + 1){
            return query(rightTreeIndex,mid + 1,r,queryL,queryR);
        }else if(queryR <= mid){
            return query(leftTreeIndex,l,mid,queryL,queryR);
        }


        E leftResult = query(leftTreeIndex,l,mid,queryL,mid);
        E rightResult = query(rightTreeIndex,mid+1,r,mid+1,queryR);

        return merger.merge(leftResult,rightResult);
    }

    public void set(int index , E e){

        if(index < 0 || index >= data.length){
            throw new IllegalArgumentException("Index is illegal");
        }

        data[index] = e;
        set(0,0,data.length - 1,index,e);

    }


    private void set(int treeIndex,int l,int r,int index, E e){

        if(l == r){
            tree[treeIndex] = e;
            return;
        }

        int mid = l + ( r - l ) / 2;
        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);


        if(index >= mid + 1){
            set(rightTreeIndex,mid + 1 ,r ,index, e);
        }else{
            set(leftTreeIndex,l,mid,index,e);
        }

        tree[treeIndex] = merger.merge(tree[leftTreeIndex],tree[rightTreeIndex]);

    }


    @Override
    public String toString(){
        StringBuilder builder = new StringBuilder();
        builder.append('[');
        for (int i = 0; i < tree.length; i++) {
            if(Objects.nonNull(tree[i])){
                builder.append(tree[i]);
            }else{
                builder.append("null");
            }

            if(i != tree.length - 1){
                builder.append(", ");
            }
        }

        builder.append(']');

        return builder.toString();

    }
}
